Recently, in order to prevent an excess loading on large vehicles, such as trucks, it has been proposed to incorporate a load measuring apparatus directly in the vehicle body to enable a driver or loading people to easily determine a loadage.
For example, as shown in FIGS. 5 and 6, there is a vehicle load measuring apparatus in a large vehicle having a suspension structure consisting of leaf springs 26a and 26b, wherein load sensors 7a, 7b of a magnetostrictive type distortion sensor or distortion sensor are attached to members which receive a load given by a weight of loaded goods. More specifically, at the side of a front wheel 25, the sensor is attached to a shackle pin 34, which connects a bracket 31 and a shackle 32; and, at the side of a rear wheel 20, the sensor is attached to a trunnion shaft 3, which is supported by a trunnion bracket 2, so that loads applied to these members can be detected, thereby measuring the loadage and/or the vehicle weight.
Specifically, as shown in FIGS. 5 and 6, the load at the side of the front wheel 25 is detected by the load sensor 7a in such a manner that an axial hole 6 is provided along an axial direction on a center line of the shackle pin 34 which connects the suspension (leaf spring) 26a of the vehicle and the bracket 31 on the side of a loading platform frame 1 through a bush 33, and a pair of sensors 7a is disposed in the axial hole 6, so as to detect distortion of the shackle pin 34 which is deformed by an amount in proportion to the load above the spring of the vehicle at the side of the front wheel 25.
On the other hand, the load at the side of the rear wheel 20 is detected by the load sensor 7b in such a manner that, as shown in FIGS. 5 and 7, the axial hole 6' is provided along an axial direction on a central line of a horizontal axis 3a of the trunnion shaft 3 engaged with the trunnion bracket 2 attached to the loading platform frame 1, and the load sensor 7b is disposed in the axial hole 6', thereby detecting distortion of the trunnion shaft 3 which is deformed by an amount in proportion to the load above the spring of the vehicle at the side of the rear wheel 20. Output signals respectively provided by the sensors 7a, 7b are amplified by amplifiers 41a, 41b to obtain the load above the springs of the vehicle. Then, arithmetic computation of adding a load below the spring of the vehicle is carried out by a controller 40, to measure the vehicle load and/or the loadage, and, if necessary, the measured value is displayed on a display device 42.
Specifically, the controller 40 performs a predetermined process based on the detected signals representing the vehicle load, a switching signal from each switch, which will be described hereinafter, and an input signal, such as, a signal representing a vehicle speed detected by a vehicle speed sensor, and sends the resulted signals representing the loadage and the total weight of the vehicle to the display device 42 provided in the driver's cabin. An accurate measurement, however, cannot be achieved in the foregoing system while the vehicle is running due to vibrations.
The above-described system has the following problems.
The vehicle speed signal is generated for example, at the time of starting the vehicle, when the vehicle speed becomes from zero (0) to a value grater than zero. The load data (the loadage and the total weight of the vehicle) is stored before starting of the vehicle. However, immediately before starting the vehicle, a minus accelerating force (a force to start) of a reaction force is produced, and the accelerating force acts upon the rear axle, thereby increasing load on the rear axle is increased, as shown in FIG. 4(a). Consequently, the load value being stored is increased up to a range of 1.about.2% depending on the condition of the loading.
Further, a similar problem is involved at the time of stopping the vehicle.
When stopping the vehicle, the driver steps on the brake, and when the vehicle speed becomes zero (0), the wheel tires come to a stop first. However, an inertial force due to the weight of the vehicle body and the loaded goods continues to advance forward. As a result, the load applied to the front axle is correspondingly increased as shown in FIG. 4(C).
In view of the above problems, the applicant of this application had considered a possibility of using load data after the lapse of a predetermined time of a few seconds after the vehicle speed has reached zero (0). However, in such measuring procedure, when the brake is continuously under the stepped-on condition, the axle is slightly distorted due to the inertial force of the vehicle body caused by holding the brake. If such a slight distortion of the axle is maintained, a reduced load is displayed. Such reduction of load is, for example, in the order of 4%.
Further, measuring of fluctuations in the loadage is made based on the load data stored immediately before starting of the vehicle or at the time of stopping the vehicle. Therefore, the above-described error values are accumulated every time when the vehicle is started or stopped by the brake action, and the eventual error will greatly exceed a predetermined range.
Thus, it is an object of the present invention to solve such problems of the prior art by providing a vehicle load measuring apparatus capable of eliminating the error caused by the above-described accelerating force at the time of starting the vehicle or the inertial force at the time of stopping the vehicle, so that an accurate and stable load data can be always stored or displayed.